The present invention relates to SiAlON material compositions particularly useful for machining of heat resistant alloys.
Heat resistant alloys are generally machined at very low cutting speeds when using cemented carbide tools due to the very low machinability of heat resistant alloys in comparison to cast iron and steel. More recently developed ceramic cutting tool materials like SiAlON (U.S. Pat. No. 4,711,644, U.S. Pat. No. 4,818,635 and U.S. Pat. No. 5,370,716) or silicon carbide whisker reinforced alumina tools (U.S. Pat. No. 4,789,277 and U.S. Pat. No. 4,961,757) have significantly increased the productivity by permitting much higher cutting speeds than can be utilized when using cemented carbide tools. Silicon carbide whisker reinforced alumina tools can normally be used at higher cutting speeds than SiAlON tools due to a better chemical stability whereas SiAlON tools can be used at higher feed rates due to a better toughness behavior. Commercial SiAlON ceramic cutting tools either are pure beta SiAlON (S.sub.6 --.sub.z Al.sub.z O.sub.z N.sub.8-Z)where O&lt;z&lt;3 and intergranular phases, or beta plus alpha SiAlON [(Si,Al).sub.12 M.sub.x (O,N).sub.16 where x is between 0.1 and 2 and M can be Li, Ca, Mg, Hf, Zr, Ce, Y, Sc or other lanthanides] and intergranular phases.
U.S. Pat. No. 4,818,635 discloses a SiAlON material, where the presence of polytype of SiAlON together with beta and/or alpha SiAlON constitutes the main components.
U.S. Pat. No. 5,370,716 claims a ceramic metal cutting material consisting of SiAlON grains and an intergranular phase. Preferably 70% of the SiAlON grains consist of beta SiAlON, Si.sub.6 --.sub.z Al.sub.z O.sub.z N.sub.8-z, with z values between 1.5 and 3.